[Sysadmins] Timing automated batch jobs ...

Mícheál Ó Foghlú mofoghlu at tssg.org
Fri Sep 18 10:11:38 IST 2009


Hi David,

That's funny!

I always thought of the Poisson as a good statistical way to simulate  
the arrivals of events to be processed in a simulation environment,  
not an operational one.
So it is an attempt to statistically re-create what (arguably) happens  
naturally when, for example, people arrive at a post office looking to  
conduct a transaction.
Thus I find it funny that it, in these special circumstances, it is  
being used operationally and not just for simulation.
I see that it is linked to when people do measurements.... ummm...  
must chat to you about this :-)

Thanks,
Mícheál

On 17 Sep 2009, at 20:46, David Malone wrote:

> On Tue, Sep 15, 2009 at 12:27:25PM +0100, Colm MacC?rthaigh wrote:
>> For some reason, I keep coming across the pattern of cron jobs that
>> have "sleep $RANDOM % 3600" in them - in a vain attempt to spread
>> load. It's a really harmful dangerous pattern, it annoyed me so much,
>> that I've written about it ;
>
> There is a pattern like this that is useful, which is to use a
> Poisson arrival process for a cron job. This is sometimes used when
> people do measurements, because it has some nice statistical
> properties (look for "PASTA" - Poisson Arrivals see Time Averages).
> This would look something like:
>
> 	sleep -3600*log($RANDOM/MAX_RANDOM)
>
> but would only be used in somewhat specialist circumstances. I think
> that RIPE TT boxes use this for doing their measurements.
>
> 	David.
>
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